Equalization for carrier systems



I Dec. 9, v CARPE EQUALIZATION FOR CARRIER SYSTEMS File d Jyily 2, 1929INVENTOR mmlilg ATTORN EY Patented Dec. 9, 1930 UNITED STATES PATENTOFFICE" 7 ALLEN CAB-PE, or NEW YORK, N. Y., ASSIGNOR 'ro AMERICAN'rELnrnoNE AND TELE- own column, a CORPORATION or NEW Your:

EQUALIZATION son canamn sYsrmrs Application filed Jul 2, 1929.: serial1e. 375,463.

This invention relates to the equalization of carrier systems sothat'all channels will be brought to substantially a common transmissionlevel, the common level being maintained constant. with changes intransmission con ditions. 7.

In a transmission conductors, the attenuation of the current valies-withfrequency, the attenuation increasing as the frequency goes up.Thisbecomes a very series matter in a multiplex carrier system, as thechannels having the higher carrier frequencies will be much moreattenuated than the channels transmitting at lower carrier frequencies.If, in such a system, the attenuation is plotted against frequency,-the

resultant curve will,ewithin reasonable fre- 'quency limits, approximatea straight line having a slope depending upon the character of thecircuit and-the existing transmission conditions. This slope varies withdifferent transmission conditions, and the variation in slope will,moreover, be different for different types of circuits.

a The need of compensation so that the transmissionat a given frequencyis maintained at a desired level, and further compensation so thatall'channels are brought at all times to thatlevel, and means foraccomplishing this, are given" in the patent of Green, No. 1,743,132,January '14, 1930. More specifically, in that application use is made oftwo pilot "frequencies existing on the pilot line at all timesfone ofthese being usedto control the gain introduced by repeaters,and the twotogether being used difierentially to correct for changes in the slopeof the attenuation characteristics of the "line.

This invention is an improvement on the method and means of theapplication referred to-and has for its object the simplification of thecircuit. arrangements and the elimination and consolidation of certainof the otherwise necessary apparatus. More particularly in my invention1' make use of two pilot frequencies, but instead of sending these outon the pilot line continuously, I send themalternately. In view of this,there need be but one oscillator at the transmitting "GP systememploying line frequency changed periodically in anypredeterminedmanner.Also, atithe further .terminal of the transmission line or at theintermediate repeater stations, it is sufiicient to have onereceivingcircuit for both of these frequencies, the receiver at any onestation Ibeing alternately altered, as by tuning, to be receptivefor the onepilotfrequency or the other. By suitable switching mechanism, then, it ispossible to operate on gain control mechanism or on equalization controlmechanism atone time or another, depending upon which particular pilotfrequency is being re- 7 ceived at'the v moment.

The figure of the accompanying drawing shows a circuit arrangement forcarrying out my invention. Referring more particularly to this drawing,there s shown a transmitting station A and an intermediate repeaterstation B, the two being connected by a transmission line, this linecontinuing to subsequent repeater stations. At the station A, there willbe associated apparatus for transmitting messages over the transmissionline L and apparatus'for receiving messages coming over this same line.Also, at this station, there is connected to the line an oscillator Othe frequency of which may be altered periodically in any suitablemanner, such as, for example, by connecting and disconnecting thecondenser C in parallel with the condenser 0,. This change may beproduced in any desired manner, such as by the'rotation of amake-and-break device 11 which in turn may be operated by clockmechanism. The

frequency at which this change occurs may be varied'over a wide range,but might very well be of the-order of once in five minutes As a result,there is impressed on the line L alternately twofrequencies f1 and fpref- At the station B, transmitting apparatus is associated with theline as at the station A. In addition, in the transmission line itself,there is introduced a potentiometer which controls the gain of therepeater end,- this oscillatofbemg adapted to have its Also in-the inputcircuit of the repeater R there is introduced an equalizer E by means ofwhich an adjustable loss may be introduced, which is a function of thefrequency. By suitable adjustment, then, of the potentiometer GP, it ispossible to bring the level of transmission at a givenfrequency f to anydesired value, and, by adjustment of the equalizer, it is possible tobring the level of all frequencies in the desired frequency band to thesame level, all as described in the above-mentioned patent of Green.

Associated with the output of the repeater R is a branch circuit 13associated with .the rectifier-amplifier 15. This association may beobtained in any of a number of ways, and, in the drawing, is shown as aninductive coupling from the coil 16 to the coil 17. Associated with thecoil 17 are condensers 18 and 19, the one of these, 18,'beingpermanently connected in parallel, yielding a circuit tuned to thefrequency f 0f the oscillator O. The condenser 19 is connected inparallel to 18 periodically in, a manner hereafter described, and, whenso connected, yields a circuit tuned to the frequency f Associated withthe output of the rectifier 15 is a galvanometer 21, of any suitableform such as the well known DArsonval galvanometer. The pointer 22 ofthis galvanometer will take up a position depending upon the size of thecurrent flowing through the galvanometer 21, and, as it changes itsposition, may pass over strips 24, 25 and 26, which-bars are movable andadjacent to contacts 27. 28 and 29. Adjacent to the pointer is a bar 30which, by some independent mechanism, may be pressed against the pointer22 which in turn bears on'the contact strips 24, 25 or 26 to closecontact with 27, 28 or 29, depending upon the position of the pointer22.

Associated with the contactmembers 25 and 28 is a relay circuitincluding the battery 32 and relay 33. The armature 34 of this relayengages with a ratch t wheel 36 to step this around for a purpose to bedescribed later.

The contact members 24 and 27' are associated; with a relay circuit 40includingthe battery 42 and the relays 43 and a l, these latter beingconnected inparallel. The circuit also includes a switching member 46constituting an armatureof a relay 38 which latter is included incircuit with the battery and. theratchet wheel 36.

In a similar manner, the contact members 26 and 29are associated with arelay circuit 50 including the battery 52 and the parallel relays 53 and54, and including, also, a switching member 56-which constitutes asecond, armature of: the relay 38. Finally, a third armature 59 of therelay 36 is used for connecting and disconnectingv the condenser 19.

The, relays. 4A and 54-v are used for controlling the gain controlmechanism GCM which in turn is associated in any suitable manner withthe potentiometer GP. The relay 44 operates on the potentiometer in amanner to increase the gain of the repeater, and the relay 54L operatesto decrease this gain. Similarly, the relays 43 and 53 control theequalization control mechanism ECM to step the equalizer E in the onedirection or the other.

The ratchet wheel 36 has its alternate teeth or segments connected to acommon point, and by means of the battery 39 is used to control therelay 38. Thus, when the armature 34 is in contact with one of thesegments just referred to, circuit for battery 39 will be closed and therelay 38 is operated. On the other alternate segments, however, circuit39 will be broken.

The limits of motion of the pointer 22 are determined by stops 61 and62, the stop 61 corresponding approximately to the position of theneedle for Zero current through the galvanometer, whereas the stop 62corresponds to approximately the maximum current which it is intendedshall flow through the galvanometer. With this maximum current, thepointer 22 is still above the member 26 and in position to contact withthat member upon the motion of the bar 30. The member 24, however, isfore-shortened so that the needle 22 is not in a position to contactwith it if the current through the galvanometer falls below a certainspecified minimum.

The methodof operation of the circuit will now be given. Consider thecircuit to be adjusted initially for proper gain and properequalization. In this invent, the current of either frequency f or f astaken off by the branch 13, is of such a magnitude as togivegalvanometer current which will bring the needle 22 over the member 25and periodically it will be pressed against themember 25 to closecontact with 28, and thus the circuit of relay 33 will be closed. Eachof these closures will cause the ratchet 36 to be movedone step and thusalternately opens. and closes'the circuit of relay 38.; This operationchanges the tuning, whereuponthe needle goes to zero and awaits the nextfrequency. During this wait, nothing occurs, however, in the circuits 40or 50, V

If, now, some change in the line. occurs so that the attenuation for thefrequency f increases, then the current through the galvanometer 21 isbelow normal during the reception of this frequency f t It may be thatit falls off suiiiciently to bring; the needle '22 above the member 24:.Let us consider this to occur while the relay 38 is operated, in whichcase the condenser 19 is connected in circuit andv the input, of therectifier 15 is adjusted for reception of the frequency f Upon pressureof the bar 30 the circuit 40 is; closed at 24 and 27 tomake contactthrough let the relay 44 which then operates .GCMto step up the gain ofthe potentiometer GP. 1 It will be noted that during this time thecircuit 50 cannot beoperated; As long as the needle 22 remains above themember-24, there will be an operation of the relay 44 and acorrespondingjstepping up of the potentiometer each time thatthe bar 30moves down to close :contact between 24 'and27, and, with each step thusmade, the current through the galvanometer' 21 increases and finally theneedle comes above the member 25. Upon the next movement'of the bar 30,.contactismade to operate the relay 33 which then moves the ratchet 36one ste forward, disconnecting the relay 38 and re easing its armatures.Upon this movement, thecondenser 19 is disconnected and the input-of therectifier 15 is now in tune for the frequency 72. If the frequency f isstillbeing given by theoscillator O, the current in the galvanometerwillfail to practically zero value, and no operation of the circuitswill occur. :In due course, however, the frequency of U willbe changedto f, and substantial current will now flow through the galvanometer 21,bringingtheneedle over, let us say, the member 24. If it stays over thismember for an appreciable time, contact will be made through thepressure bar 30, thus closing the circuit 40 through the relay 43, thusstepping the equalizer control mechanism in such a direction as toincrease the gain over the transmission line as a whole for thefrequency f and step after step of this change will occur until thecurrent for this frefrequency f brings the pointer 22 over the member25, whereupon the ratchet 36 will be moved another step to operate therelay 37 and make it possible to close circuits for the relays 44 or 54which control GCM. In the event, however, that the gain for thisfrequency f, is already too large, the pointer 22 will quickly move overthe member 26, and, in due course, the pressure bar 30 will close thecircuit 50 through the relay 53 which will then operate on ECM in thereverse direction to decrease the gain for this particular frequency.

From the above, it is seen that through the mechanism as thus describedit is possible to control the gain either upwards or downwards for thefrequency f,, bringing this to a predetermined desired level and also toequalize the gain for the frequency f either by upward or downwardadjustment to bring it to the same level as the gain for the frequency fIf these two frequencies are chosen at appropriate points in the totalfrequency range over which equalization is desired, then the departurefrom the desired gain for all the frequencies in this band will besubstantially zero.

It should be noted that no synchronization is required between theoperation at the translaced in the speech ranges,

mitter which changes the frequency from f to f and the motion of theratchet 36; This is'made possible by the fact that no adjustments at thestation B will take place if the iwrrent-throthgh the galvanometer'isbelow a quency for which the rectifier 15 is at the time tuned; Thiscircuit will therefore await theproper change at the oscillator O andwill "then resume operation and adjust the current in' the galvanometer21 to the normal value, operating, now, upon equalization if theprevious adjustment was a gain, or vice versa;

When thisvalue is reached, the cycle'of operation will be repeated.

,Ainother advantage of having a minimum value of current below which theneedle 22 makes no contacts is that of protection of the apparatus fromfalsesignals, it being assumed that these false signals would neverattain a value comparable to those necessary for the operation of themechanism as a whole. fv While reference has been made to the-controlmechanism for one ,pair'oftwires only, it is to be understood that ifthere are aplurality of such pairs of wires, each having a repeater Rthe gain of which-is to be controlled, the one set of controls GCM I andECM may be used for all such re aters.

This invention has been descrifid specifically with reference to carrierfrequency signaling but it is equally applicable for signaling in thenormal telephone range, the two pilot frequencies selected beingsuitably "It willbe evident that many modifications and ch ng s m y e inthe details of this i i withoutd parting from the. spirit of theinvention,

For instance, instead of using inlays, it wouldbe possible to carryoutthe changes with motor apparatus, habit is t be unders ood that theseand oth v iat-ions cemewith u he s p f hi iin entio VVhatiS claimed is:Y v 1. In a 'm'ultivfrequencytern,"a transmission line, the method ofequalilation of the transmission over arange of; frequencies, whichconsists in transmitting two pilot frequencies alternately, observingthe amplitudes of these after transmission, adjustingthe gain for allfrequencies in accordance with and byone of these observations, andadjusting the frequency equalization in accordance with and by theotherobservation to make the transmission equivalent of the system the sameat all frequencies.

2. In a multiffrequencysignaling system,

a transmission line, means for transmitting over the line a plurality ofpilot frequencies in sequence, means at a repeater intfor observing theamplitude of the received pilot requ ncies, a d-me ns con rolledhy in- Itransmission syscoming pilot signals for introducing gain or loss inproportion to these amplitudes to bring the levelof transmission for theclifferent frequencies to a desired value.

' 3. In a multi-frequency signaling system, a transmission line, meansfor transmitting over the line a plurality of pilot frequencies insequence, means at a repeater point for observing the amplitude of thereceived pilot frequencies, and means controlled by the pilot signalsfor introducing gain for all frequencies in accordance with theamplitude of one of the pilot frequencies, and for introducingequalization in proportion to another observed amplitude.

4. In a multi-frequency signaling system, a transmission line, means fortransmitting over the line two pilot frequencies alternately,' means ata repeater point for observing the amplitude of the received pilotfrequencies, and means for introducing gain for all frequencies inaccordance with the amplitude of and controlled by one of the pilotfrequencies, and means for introducing equalization in proportion to andcontrolled by the other observed amplitude.

5. In a multi-frequency signaling system, a transmission line, means fortransmitting alternately over the line two pilot frequencies, means at aremote point on the line for receiving these, again control mechanism,and an equalization control mechanism, and means for automaticallycontrolling these alternately in proportion to the amplitude of and bythe received pilot frequencies.

6. In a multi-frequency signaling system, a transmission line, means fortransmitting alternately over the line two pilot frequencies, means at aremotepoint on the line for receiving these, again control mechanism,and an equalization control mechanism, and means for automaticallycontrolling these -alternately in proportion to the amplitude of thereceived pilot frequencies, the one mechanism being operated on and byreceipt of the one pilot frequency, and theother on and by receipt ofthe other pilot frequency.

7. In a multi-frequency signaling system, a transmission line, means fortransmitting alternately over the line two pilot frequencies, both inthe signaling range, a receiver at a remote point on the line adapted toselectively receive one pilot frequency at a time, a gain controlmechanism, and an equalization control mechanism, and circuitsautomatically controlled by the pilot signals for operating upon onemechanism or the other, depending upon the pilot frequency beingreceived.

8. In a multi-frequency signaling system, a transmission line, means fortransmitting alternately over the line two pilot frequencies, both inthe signaling range, a receiver at a remote point on theline adapted toselectively receive one pilot frequency at a time,a gain controlmechanism, and an equalization control mechanism, and circuitsautomatically controlled by the pilot signals for operating upon onemechanism or the other, depending upon the pilot frequency beingreceived, and means for automatically shifting the receiver circuit tothe other pilot frequency when proper adjustment has been made for thefirst frequency.

9. In a multi-frequency signaling system, a vtransmission line, meansfor transmitting alternately over the line two pilot frequencies, bothin the signaling range, a receiving circuit adjusted at one time toeffectively receive one pilot frequency, a galvanometer associated withthe receiving circuit giving deflections in proportion to the amplitudeof the received pilot frequency, and comprising three sets of contacts;one for increasing gain; one for decreasing gain; and one for shiftingthe receiver to the other pilot frequency when adjustment in accordancewith the first pilot frequency has been made.

In testimony whereof, I have signed my name to this specification this1st day of ALLEN CARPE.

' July, 1929.

